A thread tension regulating apparatus set on an over-lock sewing machine has been equipped, for example, as in patent literature 1, with a mobile member which is driven by rotation of a thread tension unit in both a depressurizing direction and a pressurizing direction, and thus with a home position returning apparatus which is designed to have the thread tension unit return to the home position by operating home position returning levers on two sides of a swinging scope of the mobile member, respectively.
Patent Literature 1 Patent No. 2686188 Gazette
The thread tension regulating apparatus of Patent literature 1 equipped with the home position returning apparatus of the thread tension unit which is constituted as above and operates as above, is required to be equipped with the home position returning device by each of plural sets of a thread tension unit set on a dial tension shaft, and each home position returning device to be equipped with two side levers for returning to the home position respectively on both sides of the mobile member which moves in the pressuring direction and depressurizing direction. Accordingly, this device has such drawbacks as complication in structure with higher cost requirement and greater labor requirement for performing a returning operation.
In view of the above, an object of the invention is to simplify structure of a home position returning device to be annexed to a thread tension unit and make it possible to reduce cost, and also to facilitate use of an over-lock sewing machine by allowing a returning operation to be simply performed.